As disclosed in JP 11-48779A (References 1), JP 2001-301462A (Reference 2), and JP 2010-195187A (Reference 3), there is a vehicle door impact beam that is attached to the inside of a vehicle door. When an object collides with a vehicle door, a vehicle door impact beam absorbs the impact applied to the vehicle door, and prevents severe deformation of the vehicle door.
The vehicle door impact beams disclosed in References 1 and 2 are formed into a cylindrical shape. That is, each of the vehicle door impact beams includes an inner wall portion disposed on an inner panel side of a vehicle door, and an outer wall portion disposed on an outer panel side of the vehicle door. The inner wall portion and the outer wall portion are provided to extend in parallel with each other, and face each other. Each of the vehicle door impact beams includes a pair of side wall portions which are formed between the inner wall portion and the outer wall portion and connect the inner wall portion to the outer wall portion. In other words, each of the vehicle door impact beams includes a hollow portion that is surrounded by the inner wall portion, the outer wall portion, and the side wall portions. The vehicle door impact beams are made of aluminum alloy. The vehicle door impact beams are manufactured via extrusion forming.
The vehicle door impact beam disclosed in Reference 3 is provided to extend in a predetermined direction, and is formed into a groove shape that opens toward an inner panel side (refer to FIG. 3B in Reference 3). That is, the vehicle door impact beam includes a bottom wall portion which forms a bottom portion of a groove, and side wall portions which form side portions of the groove. The side wall portions are respectively connected to both end portions of the bottom wall portion in a width direction, and face each other. A flange portion is formed in an inner panel side end portion of each of the side wall portions, and extends toward the outside (the outside of a space surrounded by the bottom wall portion and the side wall portions) of the groove. A recession (grooved portion) is formed in an outer panel side surface of the bottom wall portion, and extends in a longitudinal direction of the bottom wall portion. That is, the recession opens toward an outer panel side (refer to FIG. 3A in Reference 3). The vehicle door impact beam is manufactured by pressing a bar-shaped steel plate.
Since the vehicle door impact beams disclosed in References 1 and 2 are formed into a cylindrical shape, the extrusion speed of an extrusion process is lower than that in a case where a member having an open sectional shape is extruded. It is necessary to perform a step of diagonally cutting both end portions of an extruded intermediately formed member so as to attach nuts, which are used to fix the vehicle door impact beam to a door panel, to the inner wall portion (refer to FIG. 1 in Reference 2).
Typically, an inner space of a vehicle door is narrow. Particularly, portions of a vehicle door (that is, front and rear end portions of the vehicle door), in which front and rear end portions of a vehicle door impact beam are respectively disposed, have small dimensions in a vehicle width direction. Accordingly, as described in Reference 1 or 2, in a case where a vehicle door impact beam is manufactured via extrusion forming, if the dimension of the vehicle door impact beam in the vehicle width direction is set to a small value such that the dimension is adapted to the dimension of spaces of front and rear end portions of a vehicle door in the vehicle width direction, it is necessary to increase the thickness of each wall portion of the vehicle door impact beam so as to ensure sufficient strength of the vehicle door impact beam. For this reason, the vehicle door impact beam has a relatively large weight.
In contrast, the dimension of a space at a location inside the vehicle door in the vehicle width direction, in the vicinity of which an intermediate portion of the vehicle door impact beam is disposed, is wider than those at locations at which the front and rear end portions of the vehicle door impact beam are disposed. First, an intermediately formed member extending straight is manufactured via extrusion forming. The dimension of the intermediately formed member in the vehicle width direction is larger than those of the spaces of the front and rear end portions of the vehicle door in the vehicle width direction. The dimensions of the front and rear end portions of the intermediately formed member in the vehicle width direction are decreased by compressing (pressing) the front and rear end portions of the intermediately formed member in the vehicle width direction. However, in this case, as illustrated in FIG. 15, there is a high possibility that the side wall portions are bent (buckled) inward and a space required to fix nuts becomes lost.
In a case where an object collides with a vehicle door, and a load induced by the collision is applied to the vehicle door impact beam disclosed in Reference 3, as the amount of intrusion (stroke) of the object increases, the vehicle door impact beam deforms in order for an open end side (inner panel side) of the vehicle door impact beam to be opened, and bending rigidity (impact absorbing performance) of the vehicle door impact beam decreases.